Bladder Cancer (Transitional Cell Carcinoma): Signs and Options

Transitional cell carcinoma, now more often called urothelial carcinoma, is the commonest cancer of the urinary tract in dogs (NC State Veterinary Hospital, 2024). It arises from the urothelium, the lining of the bladder and the urethra, the tube that carries urine out. It's much rarer in cats, though it does happen, and the picture is broadly similar.

The reason it masquerades as an infection is simply that it irritates the same lining a urine infection irritates, so it causes the same signs: straining to wee, going little and often, blood in the urine, and sometimes a weakened stream or accidents in the house (NC State Veterinary Hospital, 2024). To make it more confusing still, a tumour gives bacteria a foothold, so genuine secondary infections often sit on top of it. Antibiotics clear the bug, the dog improves for a week or two, and then the underlying cause reasserts itself (Merck Veterinary Manual, 2023). That on-off pattern is exactly why these cancers are so often caught late.

Here's the practical takeaway worth holding on to. One urinary infection that clears and stays cleared is just an infection. But recurrent lower-urinary signs that keep coming back despite treatment, particularly in an older dog, deserve a proper look rather than another repeat prescription. That doesn't mean every recurring infection is cancer, far from it, and most aren't. It means the pattern earns an investigation. If your pet has this story, our Urinary Health space walks through the full list of causes of recurrent urinary signs and what working them up involves, and the first job there is always to rule out an actual blockage, which is its own emergency. Bladder cancer is one possibility on that list, not the likeliest, but the one this article is about.

This is the hard part to hear, and the part that separates bladder cancer from many of the lumps we can simply remove. In dogs, urothelial carcinoma most often grows at the trigone, the small triangle at the neck of the bladder where the ureters arrive from the kidneys and the urethra leaves (NC State Veterinary Hospital, 2024). It's a busy, narrow junction. A tumour there can't be cut out with a clean margin the way a lump on the body can, because removing enough tissue would mean sacrificing the plumbing the bladder needs to work (Merck Veterinary Manual, 2023). Tumours sitting at the trigone, urethra or prostate are also the ones most likely to cause a dangerous obstruction.

So for most dogs, surgery isn't a cure. That's a genuinely different situation from, say, a skin tumour, and it reframes the whole goal: not "cut it out and clear it", but "control it well and keep your dog comfortable for as long as we can". That shift in aim is worth making early, because it changes which questions matter.

Reaching a confident diagnosis usually means a scan, an ultrasound of the bladder to see the mass, where it sits and whether it's spread, sometimes with a chest X-ray to check the lungs (Merck Veterinary Manual, 2023). Confirming what it is can be done by sampling cells, through a urine catheter, by cystoscopy (a camera into the bladder), or occasionally a tissue biopsy.

There's one important nuance. Vets are wary of pushing a needle through the body wall into a suspected bladder tumour, because there's a real risk of seeding cancer cells along the needle track, so this isn't routinely done (Merck Veterinary Manual, 2023). That's where a clever, non-invasive option comes in. The CADET BRAF test looks for a specific genetic mutation, present in most of these tumours, in a free-catch urine sample, the sort you collect off the floor or in a clean tray (American Kennel Club, 2019). It's sensitive enough to flag the cancer from as few as ten tumour cells in the urine, can sometimes detect it up to four months before signs appear, and the assay identifies around 85% of cases (Antech Diagnostics, 2024; American Kennel Club, 2019). A reflex add-on test, CADET BRAF-PLUS, catches more of the rest, taking the combined sensitivity to over 95% for eligible samples (Antech Diagnostics, 2024). It isn't perfect and a negative result doesn't completely rule cancer out, but it's a gentle, useful tool, especially when invasive sampling feels like a lot to put your dog through.

This is where the hard truth and the hope sit side by side. We usually can't cure this cancer, but we can often slow it down and ease the signs for a meaningful stretch, and most dogs feel well while we do.

The backbone of treatment is a particular kind of anti-inflammatory. NSAIDs in the piroxicam family don't just relieve discomfort, they appear to have a genuine anti-tumour effect against this cancer through their action on an enzyme called COX-2 (Henry et al., 2003). On an NSAID alone, many dogs get a useful three to six months of comfortable time, with the signs eased (NC State Veterinary Hospital, 2024). Adding chemotherapy, commonly mitoxantrone or vinblastine alongside the NSAID, tends to do better again, with reported survival of roughly a year for dogs whose cancer is confined to the bladder, and around six months where the urethra or prostate is involved (NC State Veterinary Hospital, 2024). If the word chemotherapy makes your stomach drop, please read our piece on why pet chemotherapy isn't human chemotherapy first, because the reality is far gentler than the picture most people carry.

These are averages, not a clock, and the figures shift as research moves, so treat them as a guide rather than a sentence. Radiation, newer drugs and clinical trials are options at some specialist centres too. Throughout, keeping your dog comfortable, managing any flare-ups of infection and staying ahead of pain is its own goal, and our guide to managing pain and comfort through cancer covers that side properly.

Bladder cancer isn't random across breeds. Scottish Terriers stand out sharply, with a risk reported as roughly 18 times that of the average dog, and Shetland Sheepdogs, Beagles, West Highland White Terriers and Wire Fox Terriers are also over-represented (Scottish Terrier Club of America, 2020). Older dogs and females are affected more often (Merck Veterinary Manual, 2023). There's also decent evidence linking the cancer to certain lawn and garden chemicals: in one study of Scottish Terriers, exposure to herbicide-treated lawns raised the risk several-fold (Glickman et al., 2004). If you have one of the high-risk breeds, that's a reasonable nudge to keep them off freshly treated grass.

The single most useful thing you can do, though, is the thing this whole article keeps circling back to. Take recurring urinary signs seriously. If your dog keeps straining or passing blood and the infection keeps coming back, ask the question early, because the sooner this is named, the sooner the treatment that buys good time can start. And while no choice here is the wrong one, the dogs who do best are usually the ones whose owners trusted that nagging sense that this wasn't just another bout of cystitis.